This invention relates to developing devices each being removably mounted on the main body of each of electrostatic recording apparatus, such as electrophotographic copying apparatus, and more particularly it is concerned with a developing device of an electrostatic recording apparatus including a casing containing a toner which is selectively attached to the main body of the apparatus for performing recording in a desired color.
In recent years, electrostatic recording apparatus, such as electrophotographic copying apparatus, have become available which comprise a developing device removably mounted on the main body of the apparatus, and in which a plurality of developing devices each containing a toner of a different color, e.g. black, sepia and blue, are provided in reserve and a developing device of a desired color can be selectively mounted on the main body to obtain a duplicate image of a document in a desired color.
The developing device of the type described of the prior art includes a casing having a developing agent in powder form, such as a toner, sealed therein to avoid its scattering when mounted on the main body of the apparatus, and a developing sleeve adapted to come into contact with an electrostatic latent image carrier of the recording apparatus which is arranged such that a portion of its outer periphery is exposed to an opening of the casing. In the developing device of this construction, if a magnetic member, such as a paper clip or other foreign matter, such as dust, were deposited on the developing sleeve when the developing device is removed from the main body of the recording apparatus and if this developing device were mounted again on the main body of the recording apparatus to perform developing, the image of the copy of the document developed would be low in quality due to the presence of white streaks on the image or the developing device might suffer damage.
When the casing containing a toner is replenished, a toner cartridge is mounted on a toner hopper of the casing. If connections of the toner hopper and toner cartridge were of the same shape and dimensions for all the developing devices of toner of different colors, it would be possible to reduce production costs. However, this would give rise to the possibility that a toner cartridge of a color different from the color of the toner contained in the toner casing of the developing device might inadvertently be mounted on the toner hopper of the developing device. To avoid this possibility, it will be evident that if an opening and a projection were formed in the toner hopper of the developing device and the toner cartridge respectively and the toner cartridge were allowed to be mounted on the toner hopper only when the projection fitted in the recess just like a key is fitted in a keyhole, and the projection and the opening were varied in shape depending on the color of the toner, then it would be possible to accomplish the object of avoiding the possibility of inadvertently replenishing the casing with a toner of the wrong color. However, it would increase production costs to provide the toner cartridge and toner hopper with projections and openings of different shapes to signify differences in the color of the toner handled. Besides, an additional space would be required in the main body of the recording apparatus.